Generally, a hand-operated chain block hoist carries on the hand wheel an endless hand chain and on the load sheave a load chain having at its one end a hook. The hand chain, when pulled in one direction, rotates the hand wheel normally to hoist a load by the hook at an end of the load chain, or, when pulled in the other direction, rotates the hand wheel reversely to lower the load.
Hand-operated hoists, especially of the hand-operated chain block type, are so constructed that a hoist body is hung high above the ground and the hand chain is handled by a worker standing on the ground so that even if the hoist body is provided with a control mechanism operable to permit free rotation of the load sheave, he cannot operate it.
Accordingly, the hand chain must be moved to rotate the hand wheel so that the load sheave is rotated to either lift the load chain or lower it to the location of a load. However, since a reduction gear mechanism is interposed between the hand wheel and the load sheave (which transmits to the load sheave the hand wheel rotation reduced in speed), operation of the hand chain must be continued for a prolonged period of time in order to lift or lower the hoist hook. For example, in a hand-operated chain block of a one ton rating, a one meter vertical movement of the hook requires about 144 rotations of the hand wheel, requiring an extensive amount of time to lift or lower the hoist hook and bring it to a desired location, resulting in poor worker efficiency. Also, workers easily tire from the prolonged handling of the hand chain. Another problem which occurs is that workers operate the hand chain in a hurry when the hoist is not loaded which can result in disengagement of the chain from the hand wheel or jamming of the two which disables the hoist.